Solder Joint Fatigue Life Prediction Method

Abstract

A solder joint fatigue life predicting method includes: establishing a maximum temperature, a minimum temperature, and a temperature cycle frequency in a field environment; establishing a maximum temperature, a minimum temperature, and a temperature cycle frequency in a laboratory environment for accelerated testing; implementing the accelerated testing to measure test fatigue life until failure of the product; determining exponents for the ramp rate and dwell time in a novel acceleration factor equation which is represented using the ramp rates and dwell times of the field environment and the laboratory environment from profile data of the temperature cycle in the field environment, from profile data of the temperature cycle in the laboratory environment, and from test fatigue life data, and calculating an acceleration factor by plugging these exponents into the acceleration factor equation; and calculating field fatigue life of the product from the calculated acceleration factor and measured test fatigue life.

What is claimed is: 
     
         1 . A method for predicting the fatigue life of a solder joint in a product joined by soldering, the method comprising the steps of:
 establishing a maximum temperature T max     —     field , a minimum temperature T min     —     field , and a temperature cycle frequency F field  in a field environment of the product;   establishing a maximum temperature T max     —     lab , a minimum temperature T min     —     lab , and a temperature cycle frequency F lab  in a laboratory environment for accelerated testing of the product;   implementing the accelerated testing of the product to measure a test fatigue life N lab  until failure of the product;   determining exponent m 1  for the ramp rate and exponent m 2  for the dwell time in Equation 1 below, which is represented using the ramp rate Ramp field  and the dwell time Dwell field  of the field environment, and the ramp rate Ramp lab  and the dwell time Dwell lab  of the laboratory environment from profile data of a temperature cycle using the established maximum temperature T max     —     field , the minimum temperature T min     —     field , and the temperature cycle frequency F field  of the field environment, from profile data of a temperature cycle using the established maximum temperature T max     —     lab , the minimum temperature T min     —     lab , and the temperature cycle frequency F lab  of the laboratory environment, and from measured data of the test fatigue life N lab , and calculating an acceleration factor AF by plugging determined exponents m 1  and m 2  into Equation 1;
                            Equation                 1                             AF   =         (       Δ                   T   field         Δ                   T   lab         )       -   n       ×       (       Ramp   field       Ramp   lab       )       m   1       ×       (       Dwell   field       Dwell   lab       )       m   2       ×              E   a     R          (       1     T   max_field       -     1     T   max_lab         )                   (     Equation                 1     )               Δ T   field   =T   max     —     field   −T   min     —     field  
 
   Δ T   lab   =T   max     —     lab   −T   min     —     lab  
 
   
       n: Constant Determined By Solder 
       E a : Activation Energy 
       R: Boltzmann Constant
 and calculating a field fatigue life N field  of the product from the calculated acceleration factor AF and the test fatigue life N lab  (N field =AF×N lab ). 
 
     
     
         2 . The method of  claim 1 , wherein the step for calculating the acceleration factor AF further comprises, when determining the exponent m 1  for the term of the ramp rates Ramp field  and Ramp lab , determining whether or not the size of a ramp rate RampUp lab  and a ramp rate RampDown lab  for a rising temperature and a falling temperature in the temperature cycle of the laboratory environment for the ramp rate Ramp lab  are the same or different. 
     
     
         3 . The method of  claim 2 , further comprising, when it has been determined that the size of the ramp rate RampUp lab  and the ramp rate RampDown lab  for a rising temperature and a falling temperature in the temperature cycle of the laboratory environment are the same, deriving a function representing the test fatigue life N lab  using a ramp rate Ramp lab  corresponding to the ramp rate RampUp lab  or the ramp rate RampDown lab  for a rising or falling temperature, and determining a correlation between the test fatigue life N lab  and the ramp rate Ramp lab . 
     
     
         4 . The method of  claim 3 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate Ramp lab  that there is no correlation, m 1 =0, and the ramp rate term [Ramp field /Ramp lab ] m1 =1. 
     
     
         5 . The method of  claim 3 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate Ramp lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized ramp rate Ramp lab  is derived from the function representing the test fatigue life N lab  using the ramp rate Ramp lab , m 1  is determined from the slope of the linear function, and the ramp rate term [Ramp field /Ramp lab ] m1  is calculated. 
     
     
         6 . The method of  claim 2 , further comprising, when it has been determined that the size of the ramp rate RampUp lab  and the ramp rate RampDown lab  for a rising temperature and a falling temperature in the temperature cycle of the laboratory environment are different, deriving a function representing the test fatigue life N lab  using the ramp rate RampUp lab  during a rising high temperature and determining a correlation between the test fatigue life N lab  and the ramp rate RampUp lab  during a rising high temperature, and deriving a function representing the test fatigue life N lab  using the ramp rate RampDown lab  during a falling low temperature and determining a correlation between the test fatigue life N lab  and the ramp rate RampDown lab  during a falling low temperature. 
     
     
         7 . The method of  claim 6 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate during a rising high temperature RampUp lab  that there is no correlation, m 1a =0 and [RampUp field /RampUp lab ] m1a =1 for [RampUp field /RampUp lab ] m1a  constituting a portion of the ramp rate term [Ramp field /Ramp lab ] m1 . 
     
     
         8 . The method of  claim 6 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate during a rising high temperature RampUp lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized ramp rate during a rising high temperature RampUp lab  is derived from the function representing the test fatigue life N lab  using the ramp rate during a rising high temperature RampUp lab , m 1a  is determined for [RampUp field /RampUp lab ] m1a  constituting a portion of the ramp rate term [Ramp field /Ramp lab ] m1  from the slope of the linear function, and [RampUp field /RampUp lab ] m1a  is calculated. 
     
     
         9 . The method of  claim 6 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate during a falling low temperature RampDown lab  that there is no correlation, m 1b =0 and [RampDown field /RampDown lab ] m1b =1 for [RampDown field /RampDown lab ] m1b  constituting another portion of the ramp rate term [Ramp field /Ramp lab ] m1 . 
     
     
         10 . The method of  claim 6 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the ramp rate during a falling low temperature RampDown lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized ramp rate during a falling low temperature RampDown lab  is derived from the function representing the test fatigue life N lab  using the ramp rate during a falling low temperature RampDown lab , m 1b  is determined for [RampDown field /RampDown lab ] m1b  constituting another portion of the ramp rate term [Ramp field /Ramp lab ] m1  from the slope of the linear function, and [RampDown field /RampDown lab ] m1b  is calculated. 
     
     
         11 . The method of  claim 1 , wherein the step for calculating the acceleration factor AF further comprises, when determining the exponent m 2  for the term of the dwell times Dwell field  and Dwell lab , determining whether or not a dwell time Dwell_High lab  and a dwell time Dwell_Low lab  for a high temperature and a low temperature in the laboratory environment for the dwell time Dwell lab  are the same or different. 
     
     
         12 . The method of  claim 11 , further comprising, when it has been determined that the dwell time Dwell_High lab  and the dwell time Dwell_Low lab  for a high temperature and a low temperature in the laboratory environment are the same, deriving a function representing the test fatigue life N lab  using a dwell time Dwell lab  corresponding to the dwell time Dwell_High lab  or the dwell Dwell_Low lab  for a high temperature or a low temperature, and determining a correlation between the test fatigue life N lab  and the dwell time Dwell lab . 
     
     
         13 . The method of  claim 12 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time Dwell lab  that there is no correlation, m 2 =0 and the dwell time term [Dwell field /Dwell lab ] m2 =1. 
     
     
         14 . The method of  claim 12 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time Dwell lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized dwell rate Dwell lab  is derived from the function representing the test fatigue life N lab  using the dwell time Dwell lab , m 2  is determined from the slope of the linear function, and the dwell time term [Dwell field /Dwell lab ] m2  is calculated. 
     
     
         15 . The method of  claim 11 , further comprising, when it has been determined that the dwell times Dwell_High lab  and the Dwell_Low lab  for a high temperature and a low temperature in the laboratory environment are different, deriving a function representing the test fatigue life N lab  using the dwell time Dwell_High lab  for a high temperature and determining a correlation between the test fatigue life N lab  and the dwell time Dwell_High lab  for a high temperature, and deriving a function representing the test fatigue life N lab  using the dwell time Dwell_Low lab  for a low temperature and determining a correlation between the test fatigue life N lab  and the dwell time Dwell_Low lab  for a low temperature. 
     
     
         16 . The method of  claim 15 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time at high temperature Dwell_High lab  that there is no correlation, m 2 a=0 and [Dwell_High field /Dwell_High lab ] m2a =1 for [Dwell_High field /Dwell_High lab ] m2a  constituting a portion of the dwell time term [Dwell field /Dwell lab ] m2 . 
     
     
         17 . The method of  claim 15 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time at high temperature Dwell_High lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized dwell time at a high temperature Dwell_High lab  is derived from the function representing the test fatigue life N lab  using the dwell time at a high temperature Dwell_High lab , m 2 a is determined for [Dwell_High field /Dwell_High lab ] m2a  constituting a portion of the dwell time term [Dwell field /Dwell lab ] m2  from the slope of the linear function, and [Dwell_High field /Dwell_High lab ] m2a  is calculated. 
     
     
         18 . The method of  claim 15 , wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time at low temperature Dwell_Low lab  that there is no correlation, m 2 b=0 and [Dwell_Low field /Dwell_Low lab ] m2b =1 for [Dwell_Low field /Dwell_Low lab ] m2b  constituting a portion of the dwell time term [Dwell field /Dwell lab ] m2 . 
     
     
         19 . The method of  claim 15  wherein, when it has been determined in the determination of a correlation between the test fatigue life N lab  and the dwell time at low temperature Dwell_Low lab  that there is a correlation, a linear function representing a normalized test fatigue life N lab  using a normalized dwell time at a low temperature Dwell_Low lab  is derived from the function representing the test fatigue life N lab  using the dwell time at a low temperature Dwell_Low lab , m 2 b is determined for [Dwell_Low field /Dwell_Low lab ] m2b  constituting another portion of the dwell time term [Dwell/Dwell field /Dwell lab ] m2  from the slope of the linear function, and [Dwell_Low field /Dwell_Low lab ] m2b  is calculated. 
     
     
         20 . A method for predicting the fatigue life of a solder joint in a product joined by soldering, the method comprising the steps of:
 establishing a maximum temperature T max     —     field , a minimum temperature T min     —     field , and a temperature cycle frequency F field  in a field environment of the product;   establishing a maximum temperature T max      —     lab , a minimum temperature T min     —     lab , and a temperature cycle frequency F lab  in a laboratory environment for accelerated testing of the product;   implementing the accelerated testing of the product to measure a test fatigue life N lab  until failure of the product;   determining exponent m 1  for the ramp rate, exponent m 2  for the dwell time, and exponent m 3  for the minimum temperature in Equation 2 below, which is represented using the ramp rate Ramp field  and the dwell time Dwell field  of the field environment, and the ramp rate Ramp lab and the dwell time Dwell lab  of the laboratory environment from profile data of a temperature cycle using the established maximum temperature T max     —     field , the minimum temperature T min     —     field , and the temperature cycle frequency F field  of the field environment, from profile data of a temperature cycle using the established maximum temperature T max      —     lab , the minimum temperature T min     —     lab , and the temperature cycle frequency F lab  of the laboratory environment, and from the measured data of the test fatigue life N lab , and calculating an acceleration factor AF by plugging the determined exponents m 1 , m 2  and m 3  into Equation 2;
                            Equation                 2                             AF   =         (       Δ                   T   field         Δ                   T   lab         )       -   n       ×       (       Ramp   field       Ramp   lab       )       m   1       ×       (       Dwell   field       Dwell   lab       )       m   2       ×       (       Tmin   field       Tmin   lab       )       m   3       ×                         E   a     R          (       1     T   max_field       -     1     T   max_lab         )                   (     Equation                 2     )               Δ T   field   =T   max     —     field   −T   min     —     field  
 
   Δ T   lab   =T   max     —     lab   −T   min     —     lab  
 
   
       n: Constant Determined By Solder 
       E a : Activation Energy 
       R: Boltzmann Constant
 and calculating a field fatigue life N field  of the product from the calculated acceleration factor AF and the test fatigue life N lab  (N field =AF×N lab ).